1. Field of the Invention
The present invention relates to a naphthoquinone derivative and an electrophotographic photoreceptor containing the same. More particularly, the present invention relates to a naphthoquinone derivative and an electrophotographic photoreceptor containing the naphotoquinone derivative which has enhanced solubility in an organic solvent, compatibility with a binder resin, and electron transport capability.
2. Description of the Related Art
Generally, an electrophotographic photoreceptor comprises a conductive substrate and a photosensitive layer on the substrate. The photosensitive layer contains a charge-generating material, a charge-transporting material, and a binder resin.
Electrophotographic photoreceptors are classified into multi-layer photoreceptors and single-layer photoreceptors. The multi-layer photoreceptor has a functionally laminated structure in which the charge-generating material and the charge-transporting material are laminated one onto the other as separate layers. The single-layer photoreceptor has a structure in which the charge-generating material and the charge-transporting material are contained in the same layer. Among them, the multi-layer photoreceptor is mainly used.
On the other hand, attention has been paid to the single-layer photoreceptor because the manufacturing process is relatively simple and the surface of the photoreceptor is positively charged by corona discharge, thus generating a smaller quantity of ozone. Therefore, the study of the single-layer photoreceptor has been actively carried out at present.
Representative examples of the single-layer electrophotographic photoreceptor include a photoreceptor obtained by dispersing a photoconductive phthalocyanine in a resin and a photoreceptor obtained by dispersing an aggregate of thiapyrylium and polycarbonate together with a charge-transporting material in a resin. However, such photoreceptors have poor electrostatic property and restriction selection of suitable photosensitive materials due to an adverse effect of photosensitive materials on the environment. Thus, these photoreceptors are not currently used.
Recently, one of the most widely used single-layer photoreceptors has been a positive charging type photoreceptor having a photosensitive layer obtained by dispersing a charge-generating material, a hole-transporting material, and an electron-transporting material in a binder resin. Such a single-layer photoreceptor has the advantage of allowing a wide selection of materials, because of the separation of functions between the charge-generating material and the charge-transporting material. Also, the charge-generating material may be used in a low concentration, helping to enhance the functional and chemical stability of the photoreceptor.
Among the materials used in such a positive charging type single-layer photoreceptor, the electron-transporting material is considered the most important. Generally, the electron transport capability of the electron-transporting material is more than 100 times smaller than the hole transport capability of the hole-transporting material. Accordingly, the performance of a single-layer photoreceptor depends on the electron transport capability of the electron-transporting material.
Methods to manufacture an organic photoreceptor with a prolonged life using a diphenoquinone derivative, a stilbenequinone derivative, or a naphthoquinone derivative as an electron-transporting material are disclosed in U.S. Pat. Nos. 5,994,012; 6,063,534; and 5,977,389, respectively. However, when such a diphenoquinone derivative is used as an electron-transporting material, electron transport capability becomes poor. Therefore, an organic photoreceptor comprising such a diphenoquinone derivative has problems such as a decrease of a charge potential and an increase of an exposure potential when used repeatedly. On the other hand, when such a stilbenequinone derivative or naphthoquinone derivative is used as an electron-transporting material, solubility in an organic solvent, compatibility with a binder resin, and electron transport capability are not satisfactory.